The shape of a boat's hull determines how it travels through the water and the activities for which it is suited. The shape is generally chosen to fit within desired load carrying, stability, speed, and hydrodynamic parameters for the boat's intended purpose. As a boat travels through the water, its motion is typically described by one of two general modes of operation: (1) pre-planing mode, including displacement mode and semi-planing or transition mode, and (2) planing mode. How a boat transitions between these operational modes and how it behaves within a particular operational mode is a function of the shape of the hull.
In displacement mode, when the boat is moving relatively slowly through the water, the primary force that keeps the boat from sinking is buoyancy. When operating in displacement mode, the bow of the boat is typically raised out of the water while the stern is pressed down into the water.
In semi-planing mode, the hull is traveling at sufficient speed to generate a moderate amount of hydrodynamic lift, but the primary force that supports the boat's weight is still buoyancy.
In planing mode, the hull generates even more lift so that the primary forces supporting the boat's weight are hydrodynamic rather than buoyant. These hydrodynamic forces tend to lift the running surface out of the water, thereby reducing drag.
Certain hull designs are specifically geared to perform in only one of these three operational modes. However, boats that are designed for skiing or wake sports water should be configured to operate well in all three modes so that the boat is adaptable to different activities such as cruising, waterskiing, wakeboarding, and/or wake surfing. For example, it may be best to operate in displacement or semi-planing mode when pulling a wakeboarder, because the wake produced in these modes is typically more substantial than the wake produced in planing mode. In contrast, for waterskiing, it may be best to operate in planing mode so that the wake is as small as possible. Often times, individual water sports performers will even prefer for the wake to be tuned to their particular preferences. Unfortunately, although many water sports boats operate well through all three operational modes, there are still very few boats that are capable of fine-tuning the wake pattern to meet each performer's personal preferences.